This Non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 092130681 filed in Taiwan, Republic of China on Nov. 4, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The invention relates to a fan, and more particularly to a centrifugal fan.
2. Description of the Related Art
A conventional centrifugal fan, as disclosed in U.S. Pat. No. 5,813,831, is mainly composed of a hub (not shown) and a plurality of blades 11, as shown in FIGS. 1a and 1b. The hub secures the fan and enables the fan to rotate about a rotation shaft (not shown). Each blade 11 has a paraxial end mounted to an outer circumference of the hub. The blades may be divided into forward leaning blades (FIG. 1a) and backward leaning blades (FIG. 1b) in terms of their arrangement manners.
However, the above-mentioned centrifugal fan still has several drawbacks to be improved. For example, under the same rotating speeds of the fans, the fan with the forward leaning blades may output larger wind pressure and provide a better heat dissipating effect but larger loading than the fan with the backward leaning blades. Therefore, it is difficult to increase the rotating speed of the fans with the forward leaning blades. On the other hand, under the same rotating speeds of the fans, the fans with the backward leaning blades have poorer heat dissipating effect than those with the forward leaning blades and thus the rotating speeds of the fans with backward leaning blades have to be increased in order to provide the same heat dissipating effect as those with the forward leaning blades. However, the noise produced is correspondingly increased owing to the increase of the rotating speed.
Furthermore, the air passage is formed by enclosing the fan blades and the fan's outer frame and predetermined gaps exist between the fan blades and the fan's outer frame. If the gaps are too small, the blades tend to be damaged by colliding with the fan's outer frame owing to the factors such as vibration. If the gaps are too large, the sucked air may flow axially and thus cause the decompression condition such that the heat dissipating effect is deteriorated and the noise is amplified.
Also, the conventional centrifugal fan often has a reduced inlet area in order to enlarge the working area of the blade. That is, the widths at two sides of the blades are the same. Therefore, the heat dissipating effect is naturally and relatively deteriorated when the intake air quantity is reduced.
In addition, the conventional fan design is only focused on the system's heat dissipation. Nevertheless, the high temperature produced by the high speed operation of the fan motor is ignored. Hence, the fan motor tends to shut down owing to high temperature or self-protection.
In summary, it is an important objective of the invention to overcome the above-mentioned problems of the centrifugal fan.